Tensioners for flexible drive systems, and in particular for flexible drive systems comprising accessory drive systems on internal combustion engines, are well known. Such tensioners include a pulley which is biased toward the flexible drive, typically a rubber belt. The pulley is mounted to an arm which is biased towards the flexible drive (the tensioning direction) by a spring and the arm can also include means to produce a dampening force to inhibit oscillation of the arm and/or flexible drive.
While such tensioners are well known, they suffer from disadvantages in that they can be relatively large, requiring significant available mounting volume (package volume) on the engine or other device on which they are installed.
Further, while dampening the movement of the tensioner arm away from the flexible drive (the de-tensioning direction) to reduce oscillation is desired, dampening movement of the tensioner arm toward the flexible drive (the tensioning direction) inhibits the ability of the tensioner to maintain tension in the flexible drive and thus is undesired.
Also, prior art tensioners which provide frictional dampening typically provide a substantially constant frictional force, independent of the amount of displacement of the tensioner arm. In contrast, it is desired that the frictional dampening force increase as the tensioner arm is moved away from the flexible drive (the de-tensioning direction), rather than being a constant force.
Further still, the manufacture and assembly of conventional tensioners can be involved, requiring machining operations on some parts and special assembly tools with multiple assembly steps, increasing the manufacturing expense of the tensioners.
It is desired to have a tensioner which can provide relatively high tensioning forces while requiring a relatively small package volume and which can be relatively easily manufactured and assembled.